Cathodic protection anode assembly



Nov. 10, 1964 E. P. ANDERSON 3,156,637

CATHODIC' PROTECTION mom: ASSEMBLY Original Filed Nov. 14. 1960 pf 12 4ag 4 26 e 6 i9 23 .92 'I5 INVENTOR. EDWARD P. ANDERSON laq ATTORNEYSUnited States Patent 1 Claim. (Cl. 204-196) This invention relates to ahigh-pressure tight seal for sealing anode assemblies through ship hullsin cathodic protection systems.

This application is a division of co-pending application No. 68,906, nowabandoned, entitled High-Pressure Tight Seal, filed November 14, 1960.

Considerable difficulties have been encountered in the design of sealingassemblies capable of resisting highpressure for extended periods oftime without corroding when in continuous contact with sea water. Suchsevere operating conditions exist with anodes in systems forcathodically protecting ship hulls.

In cathodic protection systems, the anode is mounted on the outside ofthe ship and below the water line. Since it serves as the positiveelectrode for applying protective current between the anode and thehull, electrical connection must be made from a power supply on boardand inside the ship to the anode. Such connection is generally passedthrough the hull, and the assembly must provide for insulation of theanode from the hull, it must be sufficiently tight to resist the Waterpressure, and a further requirement is that the components thereofresist corrosion which may occur under the attack by sea water and itsdecomposition products appearing in the vicinity of the anode whenprotective current is applied.

The importance of all these requirements will be appreciated whenconsidering that, with a seal through the hull of a ship, a bore throughit cannot be avoided, so that the safety of the ship is seriouslyendangered in the event that the seal becomes damaged and leakageoccurs.

Numerous attempts have been made to provide corrosion-resistant,pressure-tight seals, and heretofore the greatest part of them is basedon the well-known principle of compression. This means that the sealingassembly includes one or more resilient members, such as packings,washers or the like, and components for compressing the packing. Suchcomponents generally include screw-threaded parts or equivalentarrangements. It is well known, however, that the pressure exerted bythis type of assembly automatically releases after a certain time.Furthermore, packings are made generally from materials which, at leastafter a certain period of time, are attached by sea water or itsdecomposition products. Since cathodic protection systems are frequentlyinstalled on large seagoing vessels which cannot be checked for defectsin the anode seals, satisfactory sealing assemblies for the anodes mustbe reliable under any circumstances for long periods of time, such asmonths and even years.

Accordingly, it is one of the main objects of the present invention toprovide a seal which fulfills the requirements set forth above.

In accordance with the invention, a new type of anode sealing assemblyis provided which eliminates the necessity of compressing packings,washers or other equivalent I resilient members by means of mechanicalcomponents.

It has been found, that a high-pressure tight seal is obtained Whenproviding an assembly which includes the elements to be sealed together,herein referred to as outer and inner elements, the elements beingshaped in such a mannot that they form a space between each other,pressureinjecting a curable plastic into the space, and simultaneouslymaintaining the injected plastic under pressure and subjecting it to acuring step. Curing is normally associated with solidification and,consequently, provided 3,156,637 Patented Nov. 10, 1964 that thepressure is maintained until the curing step is essentially terminated,the finished seal is formed by elements of the assembly with the curedplastic arranged between the elements and permanently maintained at atleast the pressure which prevailed during the curing step. It appearsthat some of the curable high-polymers, generally referred to asplastics, increase their volume during the curing step, so that thepressure prevailing in the finished product may, under circumstances,exceed the pressure which was actually applied during the injection andcuring steps.

High-polymers or plastics of the type useful for producing seals inaccordance with the invention are Well known in the art. The term, asused herein, is intended to encompass high-molecular weight artificialmaterials which, either under the action of heat, of pressure, or byaging are transferred into a permanent state of solidification. Bydefinition, this process is not reversible, i.e., the materialsgenerally become insoluble and heat-resistant; they do not exhibit theproperties of a plastic any more. It is generally assumed that theprocess of curing is associated with the formation of cross-links in themolecular structure of the material. Preferably, self-curing plasticsare used and a representative group of such materials are epoxy resins.Other suitable high-polymer compounds are polysulfide rubbers; forexample, Acme Wire Companys XK-263 with AL-lSB Activator and AL-77Hardner; Minnesota Mining and Manufacturing Companys EC1130 resin andEC-776 primer with their accelerator; and Products Research CompanysPR-IZOL with PR-1201-A accelerator.

In the preferred embodiment, the high-pressure tight seal for cathodicprotection systems includes an outer gland open at both ends and adaptedto be mounted in a bore through a hull of a ship. Each of the ends ofthe gland receives an insulating plug fitted into it. The outer plugassumes the function of a support for the electrode serving as the anodeand may be maintained in its position with respect to the hull by anysuitable means, such as screw studs, or the like. A lead-in conductorconnected to the electrode passes through the outer plug, through thespace within the gland, and through the inner plug for connection to thepower supply on board the ship. The remaining space around the lead-inconductor, delimited by the inner plug surfaces and the inner Wall ofthe gland, contains a pressurized cured synthetic highpolymer orplastic. As a result of the fact that plastic was pressure-injected andcured, an effective seal is achieved.

Preferably, the gland is provided with radial bores connecting the innerspace defined between the plugs with the outer atmosphere. One of thebores may receive a self-sealing filling plug and is used forpressure-injecting the plastic from outside into the space. The otherbore serves as a vent at the beginning of the injecting step and can beclosed, for example by means of a screw, when the space is entirelyfilled out, so that the subsequently applied injection-pressure drivethe plastic between all mating surfaces to form, upon curing of thematerial, a seal under permanent pressure.

As stated above, it has been found that seals of the type contemplatedherein are particularly useful in cathodic protection systems inasmuchas one of the plugs mentioned above may constitute the support for anelectrode serving as the anode. A cathodic protection anode which mayreadily be adapted for use in connection with the seal disclosed hereinis described in US. Patent No. 3,022,243, dated February 20, 1962.However, the anode described in that patent is illustrated therein inconnection with a compression seal of which the deficiencies areovercome by the present invention. Consequently, the assembly describedherein constitutes a further development of that disclosed in theabove-mentioned Patent No. 3,022,243 as far as anode assemblies forcathodic protection systems are concerned. In other words, while themanner in which the electrode is secured to the plastic support formingone plug of the sealing assembly is essentially similar with thatdescribed in the above-mentioned patent, and the present invention isdirected to a novel seal and a manner of producing it which may becombined, for example, with the cathodic protection anode support shownin the above patent.

Other objects and advantages of the invention will become apparent fromthe following detailed description and from the accompanying drawing,which is a sectional view through one embodiment of a sealing assemblyin accordance with the invention and illustrates its use as a cathodicprotection anode assembly.

The assembly shown in the drawing includes a cylindrical gland 10,welded into a bore through the hull l2, and a plastic body 14 whichsupports the electrode performing as an anode in a cathodic protectionsystem.

The insulating support 14 has a shape similar to that of a mushroomincluding a flat circular plate 16 and a cylindrical stem 18 attached toits center. A connector pin 20 is axially embedded through the stem 13and the plate 16. The side of the support plate 16 with the stem 18thereon faces the hull 12, with an insulating blanket 19 therebetween,while the opposite side carries a corrosion resistant disc or thin plate22, generally a circular platinum sheet or a similar sheet of a platinumalloy. Good results have been obtained when using an alloy of about 50percent by weight of platinum with about 50 percent by weight ofpalladium. The thickness of the disc may be about 0.020 inch. Acomparatively narrow circumferential area of the disc is bent out of theplane of the disc and the rim 24 so obtained is embedded in the plate 16of the support to provide a firm grip all around the circumference ofthe anode disc.

The disc 22 has one additional area bent out of its plane to form acup-shaped recess with a perforated annular wall 26 and a bottom 28. Thebottom portion is Welded to a flange 30 which, in turn, forms part ofthe connector pin 20. The cup-shaped recess is filled with plasticmaterial, preferably the same as that from which the support 16 isformed, suitable polytetrafluoroethylene, or any other similar materialcapable of forming a bond with the material of the support 16.Perforations 32 through the wall portion 26 permit bonding of theplastic material inside the recess with that outside the recess. In thedrawing, the plastic material in the recess is shown partly broken awayto facilitate illustration of the perforations. Since the perforations32 are radially arranged through the wall 26, the recessed area isanchored in the support to effectively resist movement in any direction.With the circumferential rim 24 and the central area in the shape of theperforated recess embedded and anchored in the plastic, the annular areaof the disc 22 located between them and contacting the outer surface ofthe support plate 16 is maintained firmly against that surface.

The fiat circular plate 16 is provided with bores and counterboresthrough which pass threaded studs 34 welded to the hull 12. By means ofnuts 36 cooperating with the studs 34, the flat plate 16 and therewithall of the components described to this point are maintained in a fixedposition With respect to the hull and to the gland 10, with thecylindrical stem 18 protruding into the gland, as shown in the drawing.

In order to produce a high-pressure tight seal in accordance with theinvention, the other, inner end of the gland is closed by means of aplug 38 of insulating, preferably plastic material threadably engagingthe inner gland wall. The plug 38 is provided with an axial borereceiving a metallic cap 40 which, in turn, has a threaded bore throughit, through which passes the protruding portion of the pin 20. The capis preferably shaped in such a manner that its portion protruding fromthe plug 38 forms a terminal 42 adapted and dimensioned for receiving afemale connector of any suitable type (not shown) to provide currentflow through the pin 20 to the platinum foil 22.

As illustrated in the drawing, the plug 38 on one side, and thecylindrical stem 18 on the other side, are dimensioned sufficientlyshort so that an initially empty space remains within the gland 10. Apair of bores is provided through the gland at locations adjacent theempty space, so that connection is made between the space and the outeratmosphere. A self-sealing, unidirectional-valve filling plug '4, forexample of the well known type provided with a stop valve, is mounted inone of the bores, and the other bore 46 is closed by means of a screw48.

The assembly, as described to this point, is ready for the stepsnecessary to form the seal in accordance with this invention. At first,the screw 48 is removed and the filling plug 4 is connected toconventional pressure-injection equipment of any suitable type (notshown). Subsequently, this equipment is started to operate, whereby thespace defined Within the gland between the inner surface of the plug 38and of the cylindrical stem 13, and around the pin 20, as well as theinner protruding portion of the cap 40, is filled out with the plastic.Injection is continued until the material appears outside the bore 46which, during this portion of the injection step, performs as a ventthrough which air escapes from the space inside the gland into the outeratmosphere. The outflow of material indicates that the space is entirelyfilled with plastic material. Now the screw 48 is reinserted into thebore 46, so that the space within the gland 10 is completely closed.Upon further operation of the pressure-injection equipment, the plasticwithin the gland 10 is subject to pressure; this pressure remains, evenwhen the injection step is terminated and upon removal of the injectionequipment, since the filling plug 44 is provided with a stop valve. Asnoted above, the pressure forcibly drives the plastic into all possiblyexisting cracks and between mating surfaces of all of the componentsinvolved and in contact with it. The subsequent curing step thenoperates to solidify the plastic in situ, which means when in intimatecontact with all of the surfaces involved. A certain wetting action, dueto molecular forces present and active between some plastics and metalsurfaces, assists in the formation of an extremely intimate contactunder the described conditions.

The nature of the curing step depends on the highpolymer plasticmaterial selected for the specific purpose. Preferably, a self-curingplastic is used, so that solidification and transformation into anon-plastic insoluble material occurs automatically after a certaintime. In a specific instance, an epoxy resin commercially designated asUnion Carbide ERL 2774 with Lancast A accelerator has been used, whichis a self-curing plastic. After a time period of about 30 to 45 minutescuring was terminated, resulting in a high-pressure tight,corrosionresistant seal, suitable for use as an anode in cathodicprotection systems.

Although the method for producing the seal is described in the foregoingin connection with a self-curing plastic, other curable plastics may beused, and the manner in which curing is effected depends on theproperties of the selected material. Generally speaking, any type ofcurable high-polymer may be used, provided that the curing is performedin situ, i.e., that the plastic is pressurized between the matingsurfaces to be sealed during the curing step.

It will be understood that the pressure injection and curing steps maybe performed either before or after mounting the assembly into the hullof a ship.

It will be appreciated that certain modifications may be made in thestructure described without departing from the spirit or scope of thepresent invention defined in the following claim.

What is claimed is:

An anode assembly in a cathodic protection system for a ships hullcomprising an open ended tubular gland 5 member fixed through the hull,an anode element having a plate portion fixed to the outside of thehull, said anode element having a stem portion extending into one end ofthe gland member and a connector pin embedded in said stem portion andextending through said gland member, a plug fixed in and closing theother end of the gland member, said connector pin extending through theplug, said stem portion and the plug being spaced apart to provide aspace between them within the gland member, a

pair of bores opening through the side of the gland mern- 10 her intosaid space, a filling plug threaded into one of said bores, and an airvent screw threaded into the other of said bores, said space beingfilled with a synthetic plastic which has been injected into the spaceunder pressure and cured in situ.

References Cited in the tile of this patent UNITED STATES PATENTS2,910,419 Preiser et a1 Oct. 27, 1959 2,926,128 Flower Feb. 23, 19602,949,417 Preiser et a1 Aug. 16, 1960

